For me, it looks like bad practice, because mapper newcomers don’t know about relations, and they will be too scared to touch anything in that area. Or if they aren’t scared, they will definitely break everything they touch.
But on the other hand, it is clean mapping, and in their words, easier to maintain.
So should we look at this as mapping preference that should be respected, or should we look at this as bad practice that we should try to communicate with the user? Maybe I’m way off, and this is the new way to map landcover.
@Adam_Franco is on the forum, you might have wanted to invite him? As far as I can tell from what other local mappers say, the iD editor is also good with multipolygons. Personally, I consider them nice to have. Yet, they can turn out beasts as there are traps that can only be avoided when all members are loaded, so to say, when you get into so-called sparse editing. Therefore in my opinion, they should remain small, respective to area or member count.
No, this is not new. The MP-mapping-style was used here in Germany 10 years ago, but we came to the consensus that this gives more disadvantages than advantages.
For me, it looks like bad practice, because mapper newcomers don’t know about relations, and they will be too scared to touch anything in that area. Or if they aren’t scared, they will definitely break everything they touch.
if they use id they might not notice that there are relations, and they will not necessarily break anything. With josm breaking things may be easier, but you‘ll get a warning when trying to upload. IMHO when the ways have lots of nodes, not using multipolygons makes stuff very cumbersome to edit, so in Italy we welcome multipolygons in these cases. In Germany on the other hand, many people are against multipolygons for such situations and have been converting them to glued structures of simple polygons.
What should be aimed for is simple structures, don’t make multipolygons with disjunct polygons of the same type for landuse/landcover, use the smallest possible size, as this makes it easier to understand and edit later on.
I dont think its easier to maintain. It a major PITA. If you think this is easy to maintain you are using the tools wrong.
With josm:
Take a given polygon e.g. landuse, parking, building
Make a line through that area connecting both ends to the polygon
Mark line and polygon
Press Alt-X
Done - you have split your area into two on which you may change attributes.
Show me how you gonna do this with MPs e.g. relations.
This is how i change/fix/update landuse/landcover or polygons. There is an area which is not farmland.
Split the polygon, delete or retag the half not farmland.
Relations are the major issue of brokenness and should be avoided whereever possible.
I only create MP outlines of 2 or more parts if the total nodes is greater than 1899 which is very very rarely needed. Areas such as multi part calanchi of which we have many here I combine into an MP by exception (a bunch of simple polygons in an MP relation). Some actually have names.
Per recent reading, the recommended maximum members in a (MP) relation is 300.
Flo does it right, it’s peanuts to maintain in JOSM, and the bigger they are the easier they get broken by ID in particular where a problem gets so easily solved by hitting that ‘ignore’ button **. JOSM will tell you if an MP is not fully loaded and allows fetching in 1 button push. No way in ID, though requested at GitHub.
I dont think its easier to maintain. It a major PITA. If you think this is easy to maintain you are using the tools wrong.
With josm:
Take a given polygon e.g. landuse, parking, building
Make a line through that area connecting both ends to the polygon
Mark line and polygon
Press Alt-X
Done - you have split your area into two on which you may change attributes.
take two farmlands separated by a fence and with different crop (or say one is a vineyard) and this border is not straight but quite curved (i.e. it’s reasonable it has many nodes). Now you look closer and there is actually a 2-5m wide strip of scrub you want to put in between.
You will have to detach a lot of nodes if everything is glued together.
I think the same logic could be applied in favor of relations: if they are hard to maintain, you’re doing it wrong, or the tools are bad.
The main issue isn’t MP vs. ways, it’s gluing things to roads or other features, where they don’t belong to. Ungluing a way from a road is harder than removing the way from an MP, which is what @dieterdreist was also pointing out - not with a road, but with a way with lots of nodes.
I’ve been an avid MP-user in the past and they are fairly easy to maintain in JOSM, but back then (8 or so years ago), someone wanted to “help” with iD and I realized, I better convert them to ways, because that person had major issues with iD. I can work with both, and in JOSM, both work equally well. So I think the tools we have are alright.
That’s probably one way to look at it. From a data perspective, this is great, because instead of duplicating nodes, you duplicate ways, so it saves a lot of space, but on the other hand, you end up with lots and lots of ways without attributes, and this just feels wrong to a lot of people.
I like ways and I like MPs. Both have pros and cons and people can screw up either of them. I would never argue about them and use whatever is used in my area, because both just work.
I never understood why some people glue landuses to the road. This is annoying to correct, especially because of the multiple lines on top of each other.
In any case you need to create a new “geometry” which means - planting new nodes on the map. So whats the point here? I am simply saying that collecting individual lines into relations is pretty much a tedious job and prone to error.
This is how do it - Just a 30 second artificial example splitting a larger landuse into smaller parts.
Did that myself for a little as newbie, thought it was the greatest way in reusing mapped lines, until I had to maintain it, so splitting them again and unsplitting road segments on the go too. (Less instructions in cycling as well ‘keep going straight’ at every break point, though nothing in ways is going left or right :o)))
So you agree that currently these are “broken by design” and its the fault of the tools? So why do we propose to use them more extensively before fixing the tools?
Its not - Unglueing means - You create a new geometry, with new outer edges and nodes. Nothing
simpler than that. And its not that you need to remove the line from the MP - You need to draw a NEW line, than fixup the lines at the corners, then remove the highway, and add the new line.
This is how i do it. And at everysinglestep the geometries are not compromised. Even if i forget something at any stage. You may have a stray line, you may have 2 geometries, one still glued, but you will NEVER get a broken polygon e.g. broken geometry because of forgetting to add a line, forgetting to shorten the edges which means duplicates etc.
Real world does not follow simple geometries: I personally find impossible to map a wood with a meadow inside without using MP; OSM does not have layers so in many cases MPs are the only chance.
Besides, for a “simple” plain mapping, newbies can be confused when trying to select an object with shared edges between two (or more) landcovers.
I think MP approach takes the same mental effort of editing overlapping a bunch of single closed ways. Years ago I was lazy and when I stumbled upon MPs, I simply refrained from edits, without complaining about such “weird things”.
In general, since we don’t map for rendering, we should not map for newbies.
Telling someone that “if you think this is easy to maintain, you are using the tools wrong” means, that you are probably the one using the tools wrong, because you think it’s hard to maintain. I just appied the logic the other way around. I don’t find ways or MPs hard to maintain. The only broken MPs I’ve seen recently, are really large ones, and there are tools to find those. I think I found about an equal amount of “broken” ways that should have been MPs, but people just tried to avoid them like the plague.
Believe me, I’ve been there, done that. Ungluing a way from a road is more of a PITA than dealing with an MP where the road is part of it. But it also largely depends on the size of the way/MP we’re talking about. Using alt+x tends to keep the way’s old history on the wrong way, so I usually unglue the nodes with alt+j to retain the history as good as possible. You get the same issue when splitting ways on 2 nodes with p, which is why I avoid it if I want to retain the history. If I don’t care about it, then yes, I usually just split the way, insert the new segment and delete the old one from the road - pretty much the same as working with an MP. The MP on the other hand, will not lose its history. I’m well aware, that instead of deleting one of the ways, I could swap the geometry if the history is on the wrong one, but it’s an error that can happen with ways and not with MPs.
Look, I’m not saying MPs are great and should be used everywhere, but they aren’t as bad as some people are trying to picture them and people can screw up ways and MPs equally hard.
Which editor are you using in which this is a problem? For completeness, people have mentioned JOSM and iD elsewhere, and the Scotland link above is actually talking about Merkaartor!
